1. The Field of Invention
The invention relates to a shaping drum for tire carcasses. The shaping of the carcass is a step in the manufacture of tires which consists of bringing together the recesses for receiving the beads of the tire on the drum and effecting the radial expansion of all or part of the carcass laid on the drum.
2. The Related Art
Different types of so-called “membrane-free” shaping drums exist. There are mainly two major categories: drums in which the shaping of the carcass is obtained by the pressure of a fluid directly in contact with the walls of the carcass, and drums using mechanical devices for actuating plates or other elements (which will be referred to generically by the word “plate”) constituting the receiving surface for the carcass.
What is of interest here is the manufacture of tires where the carcass is initially virtually cylindrical and has to be shaped so as to be greatly domed, the tire beads of the carcasses being axially relatively close, as is the case for certain heavy-vehicle tires, competition tires or aeroplane tires. It is easy to understand that for reasons of weight and stability during manufacture it is necessary to use the category of drums which utilize mechanical devices. However, the difficulty results, on one hand, from the very great difference in diameter between the carcass before and after shaping (which may be as much as 200%), and, on the other hand, from the very small diameter of the carcass to be shaped (such as tires intended to be mounted on rims of a diameter of 13 inches), which presupposes that the plates and their actuating mechanism occupy as little space as possible in the retracted position of the drum, but nevertheless are capable of opening out radially to a considerable extent.
Solutions have been proposed, such as that set forth in publication JP-49-13629, which describes a drum utilizing, for shaping the carcass, “plates” which are slightly domed and mounted respectively on crossed connecting rods. Although it seems reliable, such a drum cannot accept any major difference between the diameter of the receiving surface of the drum in the retracted position and the diameter of the receiving surface of the drum in the expanded position. Furthermore, the minimum diameter of the drum is not able to accept tires intended to be mounted on rims of a diameter of 13 inches, for example. In fact, the crossed connecting rods still take up a lot of space in the retracted position of the drum.
Other drums of this category solve this problem by making the plates and their expansion mechanisms take up less space in the retracted position of the drums, such as that described in publication FR-830 916, which has plates forming the receiving surface for the drum and which are actuated respectively by a gear mechanism. This gear mechanism comprises, for each plate, two pinions which cooperate with each other and which are each borne by the end of an arm comprising three parts with distinct radii of curvature, the other end of the arm being axially mobile on the body of the drum. Such a drum, owing to the complexity of the gear mechanism, cannot accept tires having different diameters of the carcass before shaping even within a narrow range.
Although distinct, but because of their overall bulk, the same observations may be applied to the expansion mechanisms as proposed in publication DE 2 300 330 and U.S. Pat. No. 3,366,526.
The invention aims to overcome all these disadvantages.
Hereafter, “axial, radial, and circumferential direction” will be understood to mean the directions parallel to the axial, radial and circumferential directions, respectively, relative to the drum axis.